The early work of Woolsey was an improvement upon the ancient art of coating marine vessels with pitch and pepper in an early documented attempt to prevent wooden hulls from being eaten or rotting. Woolsey and others came upon the idea of cheap, yet dangerous, cuprous-oxide, an established toxin, to mix with a binding agent of very low holding power. A small update of that product was developed by Scott Bader of England who modified the Woolsey technology to change the binding agent to polyester resin. This polyester resin base anti-foulant contained styrene in environmentally unacceptable levels. In addition, polyester resin has proven itself to be the major cause of water ingress damage to fiberglass and fiberglass composite hulls such as osmotic blistering. The polyester resin systems also allow quick water permeation into steel and aluminum hull surfaces causing significant hull profile changes from water induced corrosion and rusting. Osmotic blistering is identified by all marine experts as the single most expensive repair cost on a fiberglass hull. Once that "osmosis" has set in and repairs are made, the likelihood of the recurrence of this "boat pox" is very high.
Polyester resin exposure causes extensive damage of a serious and permanent nature to those exposed to the fumes of the thinning or reducing agent, styrene. In another aspect, the polyester resin, which may be used as the binder in the hull construction lay up procedure or in the outer hull coating, has been found to require resin-hardener ratio changes of a very frequent nature depending upon ambient conditions. The catalyzer (MEKP) ratio should be changed with every five degrees change in ambient temperature and must be adjusted for humidity changes as well. For example, in Miami where open boat hull lay ups are done, the current temperature changes are: low temperature 73 degrees Fahrenheit in the morning and, at 2:30 p.m., 93 degrees. Since the temperature will change 20 degrees on a typical summer day, the catalyzer (MEKP) ratio must be changed no less than four times for temperature effects.
In addition, the humidity also exerts a significant detrimental influence upon the strength of polyester resin. For example, as the dewpoint changes approximately five points, the catalyzer (MEKP) ratios should be changed. Typical value changes in Florida show a humidity of 90% in the morning and approximately 50% in the afternoon. Using the same 5 point differential change requirement, the result is eight changes in resin formulations for humidity changes combined with the four temperature caused reformulations for a total of twelve changes in a typical day.
Understanding the difficulties with polyester resin from environmental and practical standpoints, Applicant set out to develop a hull coating which would render a hull impervious to water incursion, would be safe to apply, would prevent attachment by marine organisms and which would be environmentally safe.
In developing the present invention, after a great deal of research, two general resins categories were focused upon: an epoxy modified polyester called vinyl ester and epoxy adhesive itself. Because of short shelf life concerns for vinyl ester, the Applicant selected epoxy adhesive and set to work selecting additional candidates most likely to succeed as a hull coating. The selection was narrowed to the Araldite 106/103 adhesive family produced by Ciba-Geigy. The solid ingredients were metallic copper powder/flakes and a water insoluble thixotropic agent added to cause the coating to keep its configuration while curing on a hull.
While it is known to employ thixotropic agents to maintain gelcoat shape while curing, Applicant is unaware of the use of water insoluble thixotropic agents. In fact, on page 65 of the February/March, 1992 issue of Professional Boatbuilder Magazine, Technical Editor, Bruce Pfund, cites the use of water soluble thixotropic agents as a culprit in the formation of osmotic hull blistering. Applicant has, therefore, employed, solely, water insoluble thixotropic agents.
Numerous immersion tests were done all of which proved satisfactory. Under supervised laboratory conditions, immersion tests were started using the Applicant's formulations using Araldite 103/106 adhesive. Immersion tests were done on clear plastic coupons immersed in distilled water, a highly penetrating fluid. Unacceptable levels of water penetration were found on all other types of epoxy binders.
The following prior art is known to Applicant:
U.S. Pat. No. 3,761,334 to Zondek
U.S. Pat. No. 4,468,310 to Sabins
U.S. Pat. No. 4,496,444 to Bagnulo
U.S. Pat. No. 4,772,344 to Andoe
U.S. Pat. No. 4,806,432 to Eguchi et al.
U.S. Pat. No. 4,908,275 to Tsuji et al.
None of these references teaches or suggests the inventive hull coating and method. Zondek suggests use of an epoxy paint under a metal foil. This in no way teaches or suggests the present invention. Sabins teaches an aluminum marine anode designed to prevent hull corrosion. Bagnulo teaches a method of corrosion protection including a strip or band of aluminum, zinc, magnesium or alloys thereof which is mounted on a metallic structure through the use of an electrically conductive adhesive. The present invention differs from the teachings of Bagnulo as contemplating an epoxy adhesive resin mixed with particles and/or flakes of copper as well as a thixotropic substance and coated on a hull surface.
Andoe discloses a method of protecting the hulls of marine vessels from fouling. Andoe discloses an edge sealant designed to be used as an adhesive to seal a metallic foil to a hull. While Andoe contemplates an adhesive such as vinyl ester, epoxy, silicone, polysulfides or other waterproof adhesives mixed with powdered, milled, chipped or ground copper, copper/nickel or cuprous oxide, Andoe fails to teach or suggest utilizing an epoxy adhesive resin based hull coating including, mixed therein, both copper particles and a thixotropic agent. The Andoe patent fails to recognize the advantages of the present invention.
Eguchi et al. teach a copper/foiled laminated sheet for flexible printed circuit board. This patent is believed to be of only general interest concerning the teachings of the present invention.
Tsuji et al. teach a film carrier and method of manufacturing same including a resin based film and rolled copper foil laminated thereon. Of course, Tsuji et al. fail to contemplate coating of a boat hull with an epoxy adhesive based resin mixed with copper particles and a thixotropic agent.
Applicant is also patentee in U.S. Pat. No. 5,035,759 issued Jul. 30, 1991 and U.S. Pat. No. 5,044,293 issued Sep. 3, 1991. This application has been filed within one year of the respective dates of issuance of these patents.